Imaging in health care

Contents

• What is imaging in health care

• Medical imaging techniques

• Ultrasound

• Computed tomography

• Magnetic resonance imaging

• Nuclear medicine

• Elastography

• Tactile imaging

• Photoacoustic imaging

• Thermal imaging

• Medical imaging techniques

To identify processes inside a patient’s body, a doctor makes a CT or MRI image. This has already become conventional. However, diagnosis based on medical imaging continues to improve. Scientists are discovering new techniques and improving the existing ones. The research is closely related to artificial intelligence and opportunities opened up by it.

What is imaging in health care

Imaging in health care is a method which helps assess structure of organs and their functions at the cellular and molecular level. Specialists obtain images, examine them and establish diagnoses¹.

Medical imaging has a history of over 100 years: from discovering X-rays in the late 19th century to development of modern CT and MRI devices¹.

A new stage in the history of diagnostic imaging is related to artificial intelligence (AI). Algorithms provide a digital “view” of examinations in clinical medicine²:

• identifying and assessing abnormalities in images

• identifying changes which are hard to identify manually

• predicting development of a disease and response to treatment.

A doctor assesses data provided by a smart system, obtaining new diagnostic information.

Medical imaging techniques

Medical imaging combines two domains: physics and biology. The first domain is used to obtain information about tissue treatment methods: light, sound or ionizing radiation. The second domain is used to obtain data about response of the tissue to such treatment. All information is found in the diagnostic image analyzed by a doctor.

Ultrasound

Ultrasound is the technique where ultrasonic waves are used to obtain an image³:

1. An ultrasonic sensor emits sound waves.

2. They are reflected from various body parts, creating an echo.

3. The reflected waves are registered by the sensor.

4. A moving image of organs is shown on a monitor.

The method is used in various domains ofmedicine⁴:

• diagnosis: visualization of organs, such as liver or thyroid, examining growth and development of the fetus during pregnancy

• functional area: measuring speed and direction of blood flow in blood vessels and heart

• intervention: monitoring medical manipulations such as movement of a needle in tissues.

The sensor moves on the skin. It is also inserted into the body or attached to an endoscope³.

Computed tomography

Computed tomography (CT) is an imaging technique which combines X-ray and computer technologies to obtain an image of the inside of the body⁵.

The examination is carried out in several stages.

1. An X-ray tube rotates around a patient’s body inside a gantry (a round part of the CT scanner).

2. A computer system creates a 2D cross-section image of the body with each rotation.

3. A radiologist adjusts the cross-section size: it can be from 1 to 10 mm.

In some cases, to improve visualization of anatomical structures, a contrast agent is used. The agent includes a substance that absorbs X-rays, such as iodine. The contrast agent helps distinguish between alike tissues⁷.

Magnetic resonance imaging

Magnetic resonance imaging (MRI) is a method of diagnosis which uses a magnetic field and radio waves controlled by a computer. MRI allows obtaining a detailed image of a patient’s organs and tissues⁸.

A water molecule consists of oxygen and hydrogen atoms. The center of the hydrogen atom contains a smaller particle, namely a proton. Proton properties are used for obtaining an image⁹:

1. The magnetic field makes protons take one direction.

2. Radio waves emitted periodically change the position of protons.

3. When the impact of radio waves ends, the protons return to their initial state and create a radio signal.

4. Radio signals from different protons are registered and converted into pixels of an image.

The process when a proton returns to its initial state after the impact of radio waves is called relaxation. It takes place in two planes, longitudinally and widthways. To assess how much time a proton needs in each case, T1 и T2¹⁰ indicators are used. Each of these modes is characterized by specific signal intensity and the final image.

For instance, in the T1 mode fat produces a signal with high intensity and looks bright white. However, in the T2 mode the signal is weak, and the tissue looks relatively dark. A doctor selects suitable settings to see an anatomical region in different modes¹¹.

Nuclear medicine

Nuclear medicine techniques are based on using radionuclides. Their radiation is registered by special devices12.

Diagnostic principles in nuclear medicine¹³:

1. A biological molecule used during metabolism is marked with a radionuclide. The molecule is selected based on the examination purpose.

2. The obtained radiopharmaceutical is introduced in the body, usually intravenously.

3. It is accumulated in a particular organ.

4. A special scanner or a camera registers the radionuclide distribution.

There are several diagnostic techniques in nuclear medicine¹⁴:

• Single-photon emission computed tomography (SPECT): a radiopharmaceutical emits gamma rays, and they are registered. It is used for diagnosis of cardiovascular diseases, bone diseases and neurological disorders.

• Positron emission tomography (PET): radioactive decay causes positron emission. These particles react with electrons. As a result, radiation detected by sensors is produced. PET CT is used for detecting cancer and metastases.

In some cases a source of an infection process can be unclear or unknown. This makes diagnosis and treatment difficult. Nuclear medicine helps identify the infection source¹⁵.

Elastography

Elastography is an imaging technique that enables qualitative and quantitative assessment of tissue elasticity¹⁶.

Elastography is used in health care mainly for finding liver fibrosis. Fibrosis occurs when an organ is damaged for a long time. Liver tissue is gradually replaced by the stiffer connective tissue. The functions of the organ and and blood supply to it gradually become worse. Therefore, fibrosis needs control¹⁷.

For this purpose elastography is used in combination with two methods^18,19:

• Ultrasound elastography Sound waves emitted by a sensor help assess mechanical properties of the tissue.

• Magnetic resonance elastography (MRE) MRI is combined with low-frequency sound waves to obtain a visual representation of tissue stiffness (an elastogram).

Elastography is also used for examining breasts, thyroid and prostate¹⁸.

Tactile imaging

Тактильная визуализация — это технология, которая переводит чувство прикосновения в цифровое изображение²⁰.

Tactile imaging is a technique which converts the sense of touch into a digital image²⁰.

The method is a digital analog of a a physical examination technique such as palpation. A doctor touches a patient’s body to assess the size, consistency, location and tenderness of an organ²¹.

Currently, tactile imagingsystems for examining pelvic organs are being developed. The main part of the device is a probe which is inserted into a vagina. There is a sensor on the tip of the probe which records information about pressure on tissues²².

Photoacoustic imaging

The technique is based on the photoacoustic effect²³:

1. A laser is directed to a tissue.

2. The light energy absorbed by the tissue is converted into heat.

3. Physical properties of the tissue change.

4. An ultrasound signal is produced.

The latter is registered by sensors. The data on the tissue response to light help create a diagnostic image. Photoacoustic imaging helps examine various anatomical regions²⁴:

• Brain tumors. Currently, the research is conducted with animals, because human skull is thick, which makes diagnosis difficult.

• Thyroid and breasts Research was conducted where a system provided assistance in examining blood vessels in organs.

• Experiments with mice provided information about the speed and direction of blood flow in small blood vessels in the skin. This can be useful in the diagnosis of melanoma. Photoacoustic imaging also provides information on the depth of burns.

Photoacoustic imaging is the basis of multispectral optoacoustic tomography (MSOT). The technique allows not only making an image, but also determining the content of oxygen and hemoglobin in the scanned area. Tissues with thickness of up to several centimeters can be examined²⁵.

Thermal imaging

Thermal imaging is used in medicine for registration of infrared radiation related to temperature in a particular area of the body. Temperature is a biomarker of many abnormal processes. Its changes may be related to:²⁶:

• changes in blood flow in case of trauma

• inflammation

• fever

• decline in muscle activity

• development of blood vessels within a tumor.

Images (heat maps) provide information about temperature distribution in a particular part of the body. Thermal imaging systems have been used for diagnosis of breast cancer, diabetes, neurological disorders and cardiovascular diseases. Considerable advantages are that the examination can be contactless, and there is no ionizing radiation²⁷.

IT in medical imaging

Information technologies help store and transmit medical images and related data. DICOM (Digital Imaging and Communications in Medicine), the international standard, is used for data management and exchange. DICOM interface is supported by various types of devices: diagnostic tools, a doctor’s workstation, and a printer. A single standard ensures that devices “understand” each other, and an image is successfully transferred from a CT scanner to a processed film²⁸.

The image may have a high noise level and low contrast. Sometimes artifacts are found. It is not always feasible to make a new image, especially if a patient’s condition is severe or the examination is related to radiation exposure.

Technologies help improve image quality, increase contrast, reduce noise and make artifacts less noticeable. This results in an image which is more informative for a doctor²⁹.

Software used for 3D reconstruction ensures that anatomical structures are represented to a doctor and a patient in a form that is easy to recognize. The technology uses CT slices obtained in various planes to build a 3D model of an organ³⁰.

AI and its branches (machine learning and deep learning) are used in various domains of medicine. In medical imaging they improve accuracy and speed of image interpretation. The Medical Digital Diagnostic Center (MDDC) by SberMedAI includes AI-based algorithms that improve data analysis:

• CT StrokeAI analyzes CT images of the brain made without a contrast agent and highlights areas with impaired cerebral circulation. The service identifies and assesses changes in case of a stroke.

• CT Lungs. The service identifies location and percentage of lung tissue damage in CT images in case of pneumonia. The systemdetects the smallest nodules which can be the early sign of cancer.

• Mammography. The algorithm highlights suspicious areas in digital mammograms and determines the probability of malignancy.

There are algorithms that help prepare an examination protocol. For instance, the Ultrasound service integrates data obtained from measurements and ultrasound semiotics. The technology reduces the load on doctors by eliminating “paper” work.

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